Suction roll perforation design



July 16, 1963 HL R 3,097,995

SUCTION ROLL PERFORATION DESIGN 2 Sheets-Sheet 1 Filed Jan. 6, 1956 MEJ'YZLUFE EDWARD D. BEAQHLER ZOTPUWME MvZIUQi July 16, 1963 E. D. BEACHLER SUCTION ROLL PERFORATION DESIGN 2 Sheets-Sheet 2 Filed Jan. 6. 1956 ZZZZZETYZLUT" 5 Ebwmw D. BEACHLE'R IK% United States. Patent 3,097,995 SUCTION ROLL PERFORATION DESIGN Edward D. Beachler, Beloit, Wis., assignor to Beloit Iron Works, Beloit, Wis., a corporationofWisconsin Filed Jan. 6, 1956, Ser. No. 557,786. 13 Claims. (Cl. 162-371) The instant invention relates to paper making machines, and more particularly, to an improved structure of a perforate suction roll shell for use in paper machines or the like.

Although the instant invention may have application in other arts, it will be described primarily in connection with the paper machine art in which-the instantinvention is used to particular advantage. The conventional suction roll is provided with a perforate rotating cylinder having a stationary suction box operating against the inner surface thereof. The suction box creates a relatively high vacuum which is transmitted to the sheet of pulp through the perforations in the cylinder to draw the water from the sheet and compact the same. Depending upon the particular location in the paper machine, such suction rolls may vary in diameter from about 16 inches to as much as about 60 inches; and the perforations therein are relatively small in size having diameters ranging from about to about A of an inch (depending upon the shell thickness) and having a depth (or shell thickness) ranging from aboutl inch to about 4 inches. The suction rolls of the prior art, regardless of design or manufacture, produce noise when operating at speeds of about 400 feet per minute or higher, in other words, when the rolls operate at a peripheral speed of about 400 feet per minute or higher, which will also be the speed of the paper and/ or felt passing through the machine and over such rolls. Suction rolls operating at the relatively high speeds of present-day practice, which are in the neighborhood of 2000-3000 or more feet per minute, are extremely noisy, emitting a high pitched sound which is so irritating and wearisome to the operators that most operators have found it necessary to wear earplugs.

In U.S. Patent No. 2,107,812, issued to Earl E. Berry, Lloyd Hornbostel and John E. Goodwillie, a silencing device associated with the vacuum sealing strips within the roll is suggested. This patent also points out that during experiments made by the patentees attempts were made to eliminate the sound by arranging the holes in bands helically on the shell so that each band would act as a siren, the holes of each band breaking in succession overthe packing so as to. produce a pitch above the audible range; but the patentees point out thatnumerous experiments by them demonstrated the impractibility of silencing the roll in this manner. So far as is known, noone elsehas attempted to silence the rolls by changing the hole arrangements from the universally acceptedalignmentinvolving successive rows of holes wherein each row is alignedsubstantially parallel to the axis of the roll.

A fallacy in the understanding of certain of the prior workers concerning the field of silencing suction rolls was the assumption that the frequency of the sound was a function of the number of rows of holes around the roll and the roll speed. The instant invention is, however, basedin part upon the discovery that the base frequency of noise generation is not a function of the number of rows of holes and the roll speed, but rather a function of the depth of holes. The inventionis further baseduponthe discovery that, based on the finding of the base frequency of the noise, it is possible to efiect noise cancellations between pairs of holes by calculated positioning thereof on the surface of the roll in a predetermined pattern. The intensity not the frequency is a function of the number of holes and the roll speed.

It is, therefore, an important object of the instant invention to provide an improved structure of a perforate suction roll shell for use in paper machines or. the like.

Still another object of the instant'invention isto provide an improved suction roll shell structure wherein pairs of ,holes are positioned so asto effect noise cancellations therebetween so as to decrease the amount of noise created during the operation of'the suction roll at high speeds.

Other and further objects, features and advantagesof the present invention will become apparent to those, skilled in the ant from'the following detailed disclosure thereof and the drawings attached hereto and made a part hereof;

On the drawings:

FIGURE 1 is a directivity pattern submitted for the purpose of explaining certain, theoretical considerations found to be involved in the instant invention;

FIGURE 1a is a fragmentary sectional elevational view of a suction roll shell of the type embodying the instant invention which view is shown in connection withFIG- URE 1 for purposes of explaining the theoreticalcona siderations;

FIGURE 2 is essentially a top plan diagrammatic view of a roll shell of a preferred embodiment of the instant invention; and

FIGURE 3 is a noise cancellation diagram for the embodiment of FIGURE 2.

As shown onthe drawings:

In FIGURE 1a, there is shown a press roll shell 10 having a plurality of perforations 10a, 10b, 10c, etc. therein which are covered by 'afel-t 11- as-the shell 10=rotates in the direction indicated by the arrow over a sealing strip 12 mounted in afixed suction gland13. In the suction area side A a high vacuum is applied to the inside peripheryof the roll shell 10 which results in the creation of a high vacuum in perforations such as theperforation 10c. This high vacuum is retained in the hole 10c as it passes over the sealing strip 12, but the vacuum is lost just as the hole reaches the position of the hole 10b so thatitis opened to the atmospheric pressure side A of the sealing strip 12. It is believed that this is the source of noisein the operation of the suction roll.

Heretofore, the frequency of this noise was assumed to be a function of the number of rows of holes around the rolland the roll speed. Actually, the frequency, is rarely measured in the field; but it so happens that the press roll structure is such that the actual frequency of the noise is very close to the frequency of the holespacing and, therefore, it tends to be cut ofi by the higher intensity next succeeding hole. The result is an almost pure note with an imperfect wave-form, and the dominant frequencies measured are those of the hole spacing and its harmonics.

In experiments using a shell with a single row of holes drilledaround the circumference of the shell, noise emanations from these individual holes were measured at different speeds, and it was found that-a constant-frequency, dependent only on the depth of the hole, was obtained. Since the shell thickness for a given roll is substantially the same throughout, and-the hole depth h is likewise the same for each hole in the shell, the frequency ofthe noise emanating from each hole in a shell will be the same, and this has been found to be based on a wave length that is fourtimes the depth hof the hole.

It-is known, the V=)\/T=n)\ wherein:

V is velocity of propagation in ft./sec.; A is wavelength in it;

T is the period in sec; and

n is frequency in vibrations/ sec.

Since the hole depth h (in inches) which may range from 1 to 4 inches can be easily determined as h/ 12 ft., the

'2 a wavelength k is 4h/'l 2 or 12/ 3 on this basis; the formula for the present situation may be expressed as follows:

It nh 3T 3 wherein c is the speed of sound in air, which is about 1100 ft./sec. at ordinary temperatures.

I have thus found that noise of frequency n=3c/h or of wavelength )\=h/ 3 is created by each hole a, 10b, 10c, etc. at the instant it breaks over the sealing strip 12. The faster the shell 10 travels the greater will be the tot-a1 intensity of the noise because more holes are breaking per unit time; but the frequency and intensity of noise from each hole do not change. At very low speeds the sound level is very low because the slow opening of a hole is in itself a silencing effect. Each hole is thus a point source of sound.

Referring now to FIGURE 1, the chart indicated genenally by the reference numeral indicates sound directivity patterns in a given plane and the chart 20 plots sound loudness db (in decibels) against the angular position of the listener at a given location at the edge of a circle L around a sound source at a center C of the circle L. As suming first that the sound comes only from .a single point source at the center C, then a listener at any place at the edge of the circle L will hear sound of the same loudness of, for example, 100 decibels loudness as indicated on the chart 20. It must also be appreciated that the sound radiation is th-ree'dimensi-onal so that chart 20 may be considered a cross-section of a sphere and the listener would hear sound of 100 decibels loudness from any point on the surface of such sphere, using the given single point source C.

Using next a pair of sound sources A and E positioned near the center C, both emitting sound of the same frequency n but spaced /2 wavelength y apart, it will be found that the sound pattern may be plotted on the chart 20 as a figure 8, indicated at 8 by a heavy dashed line. An example of this would be a pair of holes each 2 inches in depth spaced axially 4 inches apart in a roll shell and breaking simultaneously over the sealing strip (with the machine direction indicated by the arrow associated with the chart 20). Because the holes A and E are spaced apart /2 wavelength along the axis of the roll (or along the 90-270 line of the chart 20) there will be noise cancellation along this line. The sounds emanating from the two holes A and B will be 180 out of phase to a listener at the point L in the chart 20. These sounds will, however, add to each other along the 0'180 line of the chart 20; so that a listener at the point L directly in front of the roll would hear noise of maximum loudness (the total loudnms for the two noise sources A and E being assumed to be 100 decibels for convenient interpretation of the chart 20). A listener along the roll bearing at the point L would hear no noise from the point sources A and E because of cancellation. It will also be appreciated that such cancellation takes place primarily along a line passing through the two points A and B, so that the sound pattern in three dimensions is actually in the shape of a torus; and a listener above the roll would also hear maximum loudness. A listener at a point L slightly ahead but to one side of the roll would hear only 85 decibels of noise intensity, as indicated in the chart 20. Actually the sound directivity pattern is not that clearly defined in practice because of echoes and other acoustical phenomena occurring in the operating room; but it is apparent that cancellation cannot be effected merely by sgafiing the holes /2 wavelength apart axially in a roll s e I have also found that, if .two point sources of sound B and D are used which are spaced apart only A wavelength, these point sounces B and D will function substantially as a single point source for practical purposes. In other words, if a pair of holes B and D of 2 inches depth are spaced axially 2 inches apart and break simultaneously over the sealing strip, the sounds coming from these two holes B and D will add rather than cancel in substantially all directions (although there is a relatively slight amount of cancellation along the line passing through the points B and D). I have found that so long as the distance x between the points B and D is of the wavelength or less, these point sources of sound will function substantially as a single point source. This has been found to be important for the purposes of the instant invention, because the point sources B and D may be caused to emit sounds that are out of phase. In other words, if the point source B emits sound 180 out of phase with the sound emitted by the point source D, and both emit sounds of the same frequency, then there will be substantial sound cancellation at the single point source of sound which is obtained as a practical matter using the points B and D. In such situation, the sound directivity pattern may be represented by the relatively small figure 8 indicated on the chart 20 in dotted line at 21. The figure 8 21 shows that there is substantial sound cancellation between the two points B and D in all directions (as long as the sounds emitted from these two points are 180 out of phase).

On the basis of the foregoing findings, I have further found that the drilled hole pattern for a perforate suction roll shell can be arranged so that there are a plurality of pairs of sound cancelling holes. As we have just indicated, the second hole of each pair of holes must be close enough to the first hole to function therewith as a single point source of sound, as in the case of the holes B and D, and the holes B and D must emit sounds that are 180 out of phase. If the holes B and D break over the sealing strip simultaneously they will, of course, emit sounds that are in phase. I have found a pattern which permits the holes B and D to break over the sealing strip in rapid succession so as to emit sounds that are 180 out of phase at a given relatively slow roll speed s in feet per minute. The instant drilled hole pattern thus involves a critical axial spacing between the holes B and D (so that they function as a single point source of sound) and also a critical peripheral spacing of the holes B and D (so that they will emit sounds that are 180 out of phase). With respect to the axial spacing it is, however, more convenient to define the position of one hole B as being within a given radius from the other hole D. In order to have the holes B and D function as a point source of sound, we have found that the hole B must be within a radius of /s of the wavelength from the hole D. Expressed in terms of the depth h of the holes (which may range from 1 to 4 inches), the hole B must be within a radius of 311/2 (inches) from the hole D. This radius in feet is 71 divided by 8.

The hole B must also be peripherally spaced from the hole D a predetermined distance in order to have sounds emitting from the two holes 180 out of phase at relatively l-ow machine speeds. As was pointed out previously, the frequency of the sound from each of the holes B and D is 30/11. The period T is, of course, 1/ n. It follows that:

In order to have the sounds 180 out of phase, one hole must break over the sealing strip T/2 sec. ahead of the other. The roll speed s in ft./min. is l2s/60 or s/S (inches/sec. The distance d which one hole must be spaced peripherally from the other for a given roll speed s in order to have the sounds 180 out of phase is thus the roll speed times one-half the period T:

A pattern wherein the distances d are set for a roll speed s of, for example, 400 ft./min. will emit a slight amount of noise as the roll .is speeded up to about 400 ht/min, at which speed substantial silencing of the noise occurs. Since the drilled "hole pattern 'is a repeating pat- V tern in the roll, as the roll speed increases above 400 "ftI/min, slight noise will againbe created'followed by substantial silencing again at 800 it/min. roll speed. As

will be appreciated, the distance d for rollspeed of 800 tit/min. is just twice the distance d for a first-cancellation roll speed of 400 t't/ In-like inanner, cancellation speeds of 120-0, 1600, 2000,2400, 2800, 3200, etc. ft./ min. are also obtained using-the pattern for afirst cancellation speed of 400 'tL/inin. It is apparent that the less thefirst cancellation speed, the closer together arethe subsequent cancellation speeds. Likewise, the less the first cancellation speed,the less the noise that can he heard inbetween subsequent cancellation speeds. The minimum practical first cancellation speed is .about 100 ft./min., be

low whichrequires an impractical number of holes in 41116 pattern from the point of view of roll design andrstrength.

Preferahlythe first cancellation speed is 400 to800 ft./ min, at which speeds at rollpattern design for strength and silencing can be obtained most readily. In orderto obtain appreciable silencing .benefits by the use of the instant pattern, the first cancellation speed should not exceed about 15 ft/ min.

The foregoing considerations apply to aprior'art drilled hole pattern such as shown and described in the aforementioned Berry et al. Patent 2,107,812. Said pattern is definedby a forward line of holes, which lines may be re ferred to by the letter w, and a rear line x of holes, both aligned parallel to'the axis of the roll; and a lefthand side line y of holes, and a right-hand side line 1 of holes, both of which are parallel linesperipherally aligned with the roll surface and axially spaced. Each hole has a diameter D of inchand a depth h of linch. In some "instances the holes may be countersunk with an :outer tapered portio'n'and the tapered portion is, of course, included in the overall depth h; but it will he appreciated less than /8 ozfthe wavelength orSh/Zinch. These holes, however, break over the sealing strip simultaneously; and these holes are followed over the sealing strip by ahole in the next row of holes. As will be appreciated, the spacing hetweenholes either axially or peripherally is defined on the basis of the spacing between the centers thereof iorthe purposes of the instantspeoification. The first now w of holes is peripherally spaced from the second row of holes by a distanced of0421 inch. For 1 inchshell thickness using theiorrnula and solving for-s, it will be: seen that the first cancellation speed torthe roll pattern is as follows:

in all 300 s (0.421)(30)(1100)'= 13,893 ft/min.

Obviously, the roll speed is is far greater than .anyspeed obtained in commercial paper machines. It should also be noted that if the same pattern (whichisa standard drilling pattern .for .prior art paper machines.) is .used on a. roll having ashell as much as 3 inches .thick, the result- .ing r011 speed s for the first cancellation'is 4631 .fi/IIli-IL, which is still .above the top operating speed fior commercial paper machines. It will also he noted that, using said by thehole 45]) -is 21750 ft./min.

drilling pattermit is hardly possible to move the second row of. holes closer to thefirst now without completely destroying the strength of the roll. Rolls in commercial usehaving said drilling pattern will be found to be extremely noisy.

Referring'n'ow toFIGURES 2 and 3 which show diagrammatically 'thefpreferre'd drilled hole pattern 40 for 'useinthe practice of the instantinvention. The pattern 40 is defined by a front line 4'1 and a rear line 42 par- :allel thereto, hoth ofsuch lines 41 and 42 being parallel to the axis .ottheroll; and a left-hand lin'e43 and right- -hand line 44 which are peripherally aligned with respect to theroll shell and parallel to each other.

The holes 45 in the pattern 40 are arranged in a repeating pattern which is typified by the position of the holes 45a, 45b,

45c and 45d. The holes .here :shown eac'hhave a diameter D of inch and a depth 'h of 3 inches (otherwise having an outer tapered portion as discussed with respect to the prior art but here omitted in top plan view).

The holes 45a, 45b, 45c, 45d, 45.2 and 45 break over the sealing strip in succession in the orderjust named. The second hole (in succession over the sealing strip is the hole 451) and this hole .is spaced (axially) from thefirst hole 45a a distance r equal to .53 inch. The

axial distance 17 between the peripherally alignedpattern lines (such :as 43 and 46) is 0.07 inch. The second hole 45b is thus within a radius of 3h /2 from the first hole 45a (and so are the third and fourth holes 45c and 45d, which are nearer .to the first hole 45a than the second hole 45b). The second hole 45b is peripherally spaced frornthe first hole 45a .by a distanced of .05 inch (and as indicated more (clearly in FIGURE 3, the third hole 45c is spaced the same distance d peripherally from the second hole 45b and the fourth hole 45d is spaced the same distance d "from the third hole 45c). Solving for the first cancellation speed s for the pattern 40 givesthe following result:

s =550 ft./min.

On this basis, the second cancellation speed is 1100 ft./min., the third cancellation speed (at which the hole 45a is canceled by thehole 45d) is 1650 ft./min., the fourth cancellation speed (at which the hole 45a is canceled by the hole 45e) is 2200 it/min, and the fifth cancellation speed (at which the hole 45a is canceled It has been found in actual practice that the pattern 40 elfects uniquely superior silencing of the suction roll.

Certain features of the pattern 40 have been .found to be significant from a structural point of view as well as the silencing feature. For example, the pattern 40 contains a plurality-of holes 45a, 45b, 45c and 45d peripherally spaced 'from each other. The second, third and fourth-holes 45b, 45c and 45d being peripherally spaced from the firsthole 45a an integer multiple of a distance It will also be noted that within a lateral dimension of r from the first hole45a, and the thindhole 450 is spaced the next greatest distance away .from the .first hole 45a. In this parallelogram the major angle .(between ab and ac.)1is 158 .(or about -160). The second .hole 45b is positioned at an angle of about 5 back of axial alignment with the first hole 45a (but may vary slightly within about 3-7 for slight variations in r It will further be noted that the holes 45b, 45c, 45d, 45:: and 451 (all of which are within a radius of 311 /2 from the hole 45a) are positioned in the pattern 40 so that a straight line (ab, ac, ad, ae and af) connects each with the first hole 45a without passing through any other hole. This results in an extremely sturdy roll structure with appropriate land areas inbetween the various holes to afford the necessary strength for the roll, and results in a noise spectrum of more uniform intensity at all frequencies. It should be noted that the holes 45a, 45 are in one generally circumferential column of holes, whereas the holes 45b, 45g are in a non-adjacent or alternate generally circumferential column; and the holes 45a and 45b are aligned in a generally axially aligned row of holes (which row is inclined to the axis so as to effect attenuation of noise).

It will be appreciated that the foregoing pattern with respect to the hole 45a is repeated for each of the other holes. Thus the hole 45d has holes 45c, 45 and 45g peripherally spaced thereafter so as to form another parallelogram in their positional arrangement. In the case of any hole, such as the hole 45d there is always another hole peripherally spaced therefrom by the distance d both ahead of the hole 45d as is the case for the hole 450 and behind the hole 45d as is the case for the hole 45a; and the holes 450 and 452 are within a radius of "311 /2 from the hole 45d. Such holes 45c and 452 are both within a lateral or axial dimension of 311 in the pattern 40.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.

Another theory has been advanced concerning the method of computing the peripheral spacing d hereinbefore defined and, although the applicant does not wish to limit his invention to this or any other particular theory, the essence of this theory is that the holes in a row such as the row 4'5a45b of FIGURE are inclined at an angle to the line 40 which is parallel to the axis of the roll and such inclination is such as to represent a value of A0: lying beyond that part of the curve for the second harmonic frequency where the attenuation increases sharply and before that part of the curve for the highest objectionable harmonic frequency where the attenuation decreases sharply. In other words, the inclination is such as to represent a value of At! such as to cause optimum attenuation of noise in the audible frequency range.

I claim as my invention:

.1. In a perforate suction roll shell for use in a paper machine, a drilled hole pattern wherein each hole has a depth 11 of 1 to 4 inches and within a radius of 3h/2 from a first hole there is a second hole peripherally spaced therefrom a distance d and a third hole periph erally spaced from the first a distance 2d, d being sh/30c, wherein c is the speed of sound in feet per second and s is the peripheral shell speed and is within the range 100 to 1500 feet per minute with the second hole being away from the first hole a greater distance than the third hole is away from the first hole.

2. In a perforate suction roll shell for use in a paper machine, a drilled hole pattern wherein each hole has a depth h of 1 to 4 inches and within a radius of 3h/2 from a first hole there is a plurality of holes peripherally spaced therefrom an integer multiple of a distance d, d being sit/30c, wherein c is the speed of sound in feet per second and s is the peripheral shell speed and is within the range 400 to 800 feet per minute with the hole one multiple of d away from said first hole being farther away laterally from said first hole than is the hole two multiples of d away from the first hole.

3. In a perforate suction roll shell for use in a paper machine, a drilled hole pattern wherein each hole has a depth h of 1 to 4 inches and within a lateral dimension of 3h/2 for each first hole there are three additional holes peripherally spaced therefrom one, two and three multiples of a distance d, d being sit/30c, wherein c is the speed of sound in feet per second and s is the peripheral shell speed and is within the range to 1500 feet per minute, said holes defining the corners of a parallelogram with the hole one multiple of d away from said first hole being the greatest distance away from said first hole.

4. In a perforate suction roll shell for use in a paper machine, a drilled hole pattern wherein each hole has a depth h of 1 to 4 inches and within a lateral dimension of 3h/2 for each first hole there are three additional holes peripherally spaced therefrom one, two and three multiples of a distance d, d being sh/ 30c, wherein c is the speed of sound in feet per second and s is the peripheral shell speed and is within the range 100 to 1500 feet per minute, said holes defining the corners of a parallelogram with the hole one multiple of 03 away from said first hole being the greatest distance away from said first hole, and the hole two multiples of d away from said first hole being the next greatest distance away from said first hole.

5. In a perforate suction roll shell for use in a paper machine, a drilled hole pattern wherein each hole has a depth [1 of 1 to 4 inches and within a radius of 311/ 2 from each hole there is a plurality of holes peripherally spaced therefrom an integer multiple of a distance d, d being sit/30c, wherein c is the speed of sound in feet per second and s is the peripheral shell speed and is within the range 100 to 1500 feet per minute, and said plurality of holes being positioned so that a straight line connects each with said first hole without passing through any other hole.

6. In a perforate suction roll shell for use in a paper machine, a drilled hole pattern wherein each hole has a depth h of 1 to 4 inches and within a lateral dimension of 3h/ 2 from each first hole there are three additional holes peripherally spaced therefrom one, two and three multiples of a distance d, d being sh/ 30c, wherein c is the speed of sound in feet per second and s is the peripheral shell speed and is within the range 100 to 1500 feet per minute, with the hole one multiple of d away from said first hole being the greatest distance away from said first hole.

7. A suction roll having in its cylindrical surface a plurality of holes arranged in a regularly recurring pattern of generally axial rows and generally circumferential columns with each row composed of holes from nonadjacent columns and each row disposed along the line equidistant from and parallel to the lines of the two adjacent rows, said lines being inclined to a line parallel with the central longitudinal axis of the roll, such inclination being such as to cause optimum attenuation of noise in the audible frequency range.

8. A suction roll having in its cylindrical surface a plurality of holes arranged in a regularly recurring pattern of generally axial rows and generally circumferential columns with each row composed of holes from alternate columns and each row disposed along a line equidistant from and parallel to the lines of the two adjacent rows, said lines being inclined to a line parallel with the central longitudinal axis of the roll, such inclination being such as to represent a value of A0: lying beyond that part of the curve for the second harmonic frequency where the attenuation increases sharply and before that part of the curve for the highest objectionable harmonic frequency where the attenuation decreases sharply.

9. In an article having an elongated surface bearing a regularly recurring pattern of rows and columns of structural deviations, with each row composed of structural deviations from non-adjacent columns, such as to give rise to noise on relative movement between said surface and a cooperating surface with which it comes into momentary contact, said rows extending generally transversely to the direction of said relative movement and said columns extending generally parallel with the direction of said relative movement; the provision of an inclination between each of said rows and the direction transverse to the direction of said relative movement, such inclination being such as to cause optimum attenuation of noise in the audible frequency range.

10. A suction roll having in its cylindrical surface a regularly recurring pattern of holes arranged in successive circumferential columns and axial rows of equally spaced holes, with the rows being composed of holes from non-adjacent columns, said rows peripherally spaced successively about said roll, a circumferential distance d, where d equals sh divided by 30c, in which s is a speed in feet per minute, h is the depth of said holes, and c is the velocity of sound in feet per second, an index row, a first succeeding row, a second succeeding row, said first succeeding row displaced axially relative to said index row, not more than a distance 3h/ 2, and not less than said second succeeding row is displaced axially with respect to said index row, said second successive row being displaced an amount intermediate to the aforesaid displacement.

11. In a combination, a straight stationary sealing strip, a suction ro ll having in its cylindrical surface a plurality of holes arranged in a regularly recurring pattern of generally axial rows and generally circumferential columns with each row composed of hole-s from non-adjacent columns, and means for rotating said roll at high speed to cause said rows of holes to pass successively beyond said sealing strip; the provision of an inclination between the line of extent of said sealing strip and the line of each row of holes such as to cause optimum attenuation of noise in the audible frequency range.

12. In a system of a type comprising a first member having an elongated surface bearing a regularly recurring patterns of rows and columns of structural deviations 'lwith each row composed of structural deviations from alternate columns, a cooperating second member having a surface, and means for effecting relative movement between said surfaces to bring them into momentary contact, whereby to give rise to noise, said rows extending generally transversely to the direction of said relative movement and said columns extending generally parallel with the direction of said relative movement; the provision of an inclination between each of said rows and the direction transverse to the direction of said relative movement, such inclination being such as to cause optimum attenuation of noise in the audible frequency range.

13. In a combination, a straight stationary sealing strip, a suction roll having in its cylindrical surface a plurality of drilled holes arranged in a regularly recurring pattern of generally axial rows and generally circumferential columns, and means for rotating said roll at high speed to cause said rows of holes to pass successively beyond said sealing strip; the provision of an inclination between the line of extent of said sealing strip and the line of each row of holes such as to cause optimum attenuation of noise in the audible frequency range; within said hole pattern each of said holes having a depth h of 1 to 4 inches and within a lateral dimension of 3h/2 for each first hole there being three additional holes peripherally spaced therefrom one, two and three multiples of a distance d, d being sh/ 30c, wherein c is the speed of sound in feet per second and s is the peripheral roll surface speed and is within the range of to 1500 feet per minute, said holes defining the corners of a parallelogram with the hole one multiple of d away from said first hole being the greatest distance away from said first hole, and the hole two multiples of d away from said first hole being the next greatest distance away from said first lhole.

References Cited in the file of this patent UNITED STATES PATENTS 1,741,974 Burden Dec. 31, 1929 1,808,493 Burden June 2, 1931 1,834,470 Millspaugh Dec. 1, 1931 1,843,876 Kilberry Feb. 2, 1932 2,069,119 Standley et a1 Jan. 26, 1937 2,107,812 Berry et a1 Feb. 8, 1938 2,274,641 Abbott et a1. Mar. 3, 1942 

13. IN A COMBINATION, A STRAIGHT STATIONARY SEALING STRIP, A SUCTION ROLL HAVING IN ITS CYLINDERICAL SURFACE A PLURALITY OF DRILLED HOLES ARRANGED IN A REGULARLY RECURRING PATTERN OF GENERALLY AXIAL ROWS AND GENERALLY CIRCUMERFERENTIAL COLUMNS, AND MEANS FOR ROTATING SAID ROLL AT HIGH SPEED TO CAUSE SAID ROWS OF HOLES TO PASS SUCCESSIVELY BEYOND SAID SEALING STRIP; THE PROVISION OF AN INCLINATION BETWEEN THE LINE OF EXTEND OF SAID SEALING STRIP AND THE LINE OF EACH ROW OF HOLES SUCH AS TO CAUSE OPTIMUM ATTENUATION OF NOISE IN THE AUDIBLE FREQUENCLY RANGE; WITHIN SaID HOLE PATTERN EACH OF SaID HOLES HAVING A DEPTH H OF 1 TO 4 INCHES AND WITHIN A LATERAL DIMENSION OF 3H/2 FOR EACH FIRST HOLE THERE BEING THREE ADDITIONAL HOLES PERIPERALLY SPACED THEREFROM ONE, TWO AND THREE MULTIPLES OF A DISTANCE D,D BEING SH/30C, WHEREIN C IS THE SPEED OF SOUND IN FEET PER SECOND AND S IS THE PERIPERAL ROLL SURFACE SPEED AND IS WITHIN THE RANGE OF 100 TO 1500 FEET PER MINUTE, SAID HOLES DEFINING THE CORNERS OF A PARALLELOGRAM WITH THE HOLE ONE MULTIPLE OF D AWAY FROM SAID FIRST HOLE, AND BEING THE GREATEST DISTANCE AWAY FROM SAID FIRST HOLE, AND THE HOLE TWO MULITIPLES OF D AWAY FROM SAID FIRST HOLE BEING THE NEXT GREATEST DISTANCE AWAY FROM SAID FIRST HOLE. 